[media] tuner-xc2028: Don't try to sleep twice

Only send a power down command for the device if it is not already
in power down state. That prevents a timeout when trying to talk
with the device.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

diff --cc drivers/media/tuners/tuner-xc2028.c
Simple merge